The stellar interferometer at Narrabri Observatory I. A. description of the instrument and the observational procedure

A stellar intensity interferometer has been installed - at Narrabri Observatory in New South Wales, and is being used to measure the angular diameters of bright stars in the spectral range 0 to F. This paper describes the instrument and the observational procedure. Experience has shown that the performance is in reasonable agreement with theory and it is concluded that the measurements of angular diameter given in Paper II are reliable.